Moving Water and Earth

Next door to the steady thrum of hydroelectric generators, Lorenz Straub’s lab served grand engineering and hydraulics experiments around the world, making possible the mastery of its great river systems. Now that the huge ecological and social costs of such projects have become clear, the wisdom of such mastery is no longer presumed, and the lab has adapted and grown. “The lab is a unique institution because of its interdisciplinary flexibility, bringing together engineers, geoscientists, and biologists,” said Sotiropoulos, explaining how the rigors and narrow focus of hydraulic science have given way to the complexities of earth science. Recently, the lab was chosen by the National Science Foundation to host the National Center for Earth-surface Dynamics, a clearinghouse for data relevant to tectonicians, volcanists, and riparian wits worldwide. NCED was created to provide a better understanding of the many processes shaping the surface of the Earth, and in contrast to the long line of civil engineers who have run the lab, the head of NCED is a geologist, Chris Paola.

Paola is not the sort of geologist who, hammer in hand, scrutinizes ancient ledges of bedrock like the limestone slabs that jut into the basement of the lab. Most often using computer models, he seeks to understand the ancient legacies of sedimentary processes. But computer modeling has its limitations, and Paola and his former colleague Gary Parker, a civil engineer, envisioned a contraption that would reproduce, in scale, the infinitesimally slow processes of geomorphology.

No one had ever built such a device before. To carry out their scheme, Paola and Parker asked an engineer at the lab, Chris Ellis, to build a basin in the laboratory that could replicate an undulating bedrock layer; on its surface, eons’ worth of stream sediment would deposit a facsimile of the layer cake that is our ancient Earth. Ellis, smart enough to see the steepness of the trail ahead, ran the concept by a longtime friend, Jim Mullin, a man with mechanical experience but no formal training. The lab, an egalitarian outpost of the University, has the institutional smarts to recognize that such puzzles are sometimes best resolved by chemistry and collaboration, and Mullin, a pure mechanical mind without a degree, was given a salary. “His involvement made the experiment work,” says Paola. “He’s the best designer I’ve ever met.” Ellis and Mullin schemed, pondered, failed, stepped back; finally, from all their bolting and welding a functioning model came into existence.

The product is a large dynamic sandbox that the lab has playfully dubbed Jurassic Tank, and its first results drew the attention of Scientific American. The name is appropriate insofar as that geological period, along with the Cretaceous, sowed the seeds of most of the earth’s petroleum reserves, and subsurface geologists like Paola have often found willing patrons in the boardrooms of oil companies. (The Platteville limestone that outcrops into the basement of the lab, Ordovician in origin, predates the Jurassic by over two hundred million years.) While it resembles any industrial bulwark ever built in the vicinity of St. Anthony Falls, the Jurassic Tank turns the Mississippi’s flow into an agent of information—and in so doing once again forestalls the falls’ decay.

As suggested by the geologic history of St. Anthony Falls, some of the earth’s most dynamic surfaces lie along and beneath rivers, and part of NCED’s mission is river restoration; one example is the removal of dams in the American West, such as the Glen Canyon Dam on the Colorado River, silted to the chin and soon to be obsolete. Other river restoration projects will soon help create a much more visible presence for the lab: outdoor experiments will be installed on the dry spillways next to the lab and meander in plain sight of joggers and tourists on the Stone Arch Bridge. (The spillways were designed to relieve flow at flood stage but have never proved necessary.) “People in the city are unaware that there is an institution with a tremendous international reputation right in their midst,” says Sotiropoulos. “This is an opportunity for us to expand our laboratory and reveal it to the community.”

Entering its seventieth year, the St. Anthony Falls Laboratory seems fit to endure, but the ground beneath it is only as good as its latest fix. Apparently, the Army Corps never completed its repair of the falls in the 1870s after the collapse of the Eastman tunnel. According to David Wiggins, who runs the National Park Service’s Mississippi River Visitor Center in St. Paul, Corps engineers suggested a second subterranean dike upstream where the limestone ends, but the work was never funded. So it is not inconceivable that parts of the falls will someday succumb to the river. In fact, this happened as recently as 1987, when the river rushed into the sandstone beneath the hydroelectric plant at the lower dam, just downstream from the Stone Arch Bridge, and collapsed parts of its floor and roof. This time, engineers commanding a fleet of trucks plugged the forty-by-six-foot gap within a day. But heroes wearing pocket protectors notwithstanding, the river just keeps rolling along.